Polyacrylic acid having high chelation value and its production

ABSTRACT

Polyacrylic acid having a high chelation value is produced by polymerizing acrylic acid at elevated temperature in the presence of an alkali metal or ammonium persulfate initiator and, in a concentration of about 0.5 to 4% by weight of the acrylic acid, a chain transfer agent selected from the group consisting of alkanethiols, hydroxy alkanethiols, and carboxy alkanethiols. Preferably the chain transfer agent is present in about 1% by weight concentration and is octanethiol, butanethiol, thioglycolic acid, or 2-thioethanol.

United States Patent [191 Shahidi et a1.

[451 Sept. 9, 1975 POLYACRYLIC ACID HAVING HIGH CHELATION VALUE AND ITSPRODUCTION [75] Inventors: Iraj Khatib Shahidi, Florham Park,

N.J.; Jorge Alberto Blay, Corpus Christi, Tex.

[73] Assignee: Celanese Corporation, New York,

[22] Filed: July 20, 1973 [21] Appl. No.: 381,190

[52] US. Cl 260/537 N; 252/109; 252/133;

252/135; 252/184; 260/526 N [51] Int. Cl. C07C 55/24 [58] Field ofSearch 260/526 N, 537 N [56] References Cited UNITED STATES PATENTS2,833,745 5/1958 Fikentscher 260/80 FOREIGN PATENTS OR APPLICATIONS695,097 8/1940 Germany ..260/537 167,857 10/1953 Australia ..260/537OTHER PUBLICATIONS Jacobson Chem. Abstracts, V. 57( 1962), V. 1037.Sakaguchi et a1. Chem. Abstracts, V. 64(1966), p. 12822.

Salutsky Chem. Abstracts, V. 70(1969), p. 248.

l-lwa et al. Chem. Abstracts, V. 7l( 1969), p. 216.

Primary Examiner.lames A. Patten Attorney, Agent, or Firm-Leonard Horn;Ralph M. Pritchett [57] ABSTRACT Polyacrylic acid having a highchelation value is produced by polymerizing acrylic acid at elevatedtemperature in the presence of an alkali metal or ammonium persulfateinitiator and, in a concentration of about 0.5 to 4% by weight of theacrylic acid, a chain transfer agent selected from the group consistingof alkanethiols, hydroxy alkanethiols, and carboxy a1- kanethiols.Preferably the chain transfer agent is present in about 1% by weightconcentration and is octanethiol, butanethiol, thioglycolic acid, or 2-thioethanol.

7 Claims, No Drawings POLYACRYLIC AID HAVING HIGH CHELATION VALUE ANDITS PRODUCTION BACKGROUND OF THE INVENTION This invention relates to theproduction of polyacrylic acid having a high chelation value, e.g., achelation value which is in excess of 500 milligrams of calciumcarbonate per gram of chelant obtained in water with a 200 ppm hardness,pH 9.5 and at the point at which 80% of the hardness has beensequestered. The significance of this 80% chelation level as an indexfor comparing various chelating agents will be explained laterhereinbelow.

Most common detergents, e.g. common household detergents, comprise, inaddition to other components, phosphates such as sodiumtripolyphosphate. These are inexpensive and effective, but their use isnow consid ered to present a water pollution problem in that thephosphate component has the undesired effect of promoting excessivegrowth of algae in lakes and streams (eutrophication).

Accordingly, there has been much research aimed at developing detergentswhich contain little or no phosphate but which will still be safe andeffective. In particular, this research has been aimed at developing detergent components which can sequester calcium, magnesium, and like ionsfound in hard water and which have an economically feasibleprice/performance ratio. Aside from effectiveness and economicfeasibility, it is also important that these detergent components befree from health hazard and that they have no adverse effects onmechanical equipment used in laundering. For example, highly alkalinedetergent components such as washing soda have effective detergentaction but are hazardous household substances because of their highalkalinity (pl-I l l or higher). There is also a question as to whetherthey may cause mechanical problems in, for example, washing machines.Likewise nitrilotriacetic acid and ethylenediaminetetraacetic acid arevery ef fective in sequestering a large amount of calcium but arerelatively expensive and, in addition, have recently been questionedfrom the health standpoint inasmuch as a question has arisen as towhether they are potentially carcinogenic.

Finally, polyacrylic acid, as such or in the saltform, has also beenproposed as a chelant or sequestering agent which does not causeeutrophication, but this material as known heretofore has been of onlymediocre effectiveness.

It has now been discovered, however, that polyacrylic acid, when made bya certain procedure which will be described hereinbelow, can be made tohave an unexpectedly high chelating value. It is, accordingly, an objectof the present invention to provide a method for producing a polyacrylicacid chelating agent which is unexpectedly effective as compared withsimilar materials known to the prior art and which will be free from thedrawbacks which are associated with those alternative detergentcomponents known to the art.

SUMMARY OF THE INVENTION In accordance with the present invention it hasbeen found that polyacrylic acid having an unexpectedly high chelatingvalue (which will be defined hereinbelow) can be produced bypolymerizing acrylic acid at elevated temperature in the presence of analkali metal or ammonium persulfate initiator and also in the presenceof about 0.5 to 4% (calculated on the basis of the weight of the acrylicacid) of a chain transfer agent selected from the group consisting ofalkanethiols, hydroxy alkanethiols, and carboxy alkanethiols. Preferablythe chain transfer agent is present in a concentration of about 1% byweight based on the acrylic acid and is a member of the group consistingof octanethiol, butanethiol, thioglycolic acid, and Z-thioethanol. Otherthiols which can be employed include methanethiol, ethanethiol,propanethiol, pentanethiol, hexanethiol, heptanethiol, nonanethiol,decanethiol, dodecanethiol, and their branched isomers, e.g.sec.-butanethiol, isopropanethiol, tert.-butanethiol, and the like, aswell as their hydroxy and carboxy substitution products, e.g.,3-mercaptopropanol, 3-mercaptopropionic acid, 6- mercaptohexanoic acidand the like.

The initiators may be present in amounts ranging from as little as about0.5 up to 10% or more by weight of acrylic acid although preferably theyare present in about 0.5 to 4%. A concentration of about 1% isespecially useful. Preferred initiators include sodium, potassium, orammonium persulfates or mixtures thereof.

The polymerization can be conducted in bulk but it is preferablyconducted in aqueous solution at a concentration of about 5 to 40% andpreferably about 10 to 30% acrylic acid by weight. The temperature maybe room temperature or lower but, since polymerization rate increaseswith temperature, the temperature is desirably elevated but below theboiling point so that special equipment will not be required, e.g. aboutC. The time will typically run about 1 to 2 hours until there issubstantially no residual free acrylic acid.

The molecular weight will directly determine the viscosity of theresulting solution, and the viscosity may range from about 25 centipoiseor lower up to 200 or more although preferably it is about 50 tocentipoise for a 2025% polyacrylic acid solution by weight.

The solutions may if desired be concentrated to any desired degree,including completely to dryness, optionally after neutralization to formsodium and/or potassium polyacrylate. Alternatively, the solution may beblended with one or more'other ingredients of a detergent composition indry or liquid state and the mixture spray or drum dried.

In assessing the effectiveness of chelating agents it is convenient toemploy a term referred to as the chelating value, the significance anddetermination of which are explained by J. A. Blay and J. H. Ryland inAnalytical Letters, Vol. 4, No. 10, pp 653-663 (1971). Numerically, thechelation value (CV) is expressed as the milligrams of calcium carbonatechelated or sequestered per gram of chelating agent. The chelationreaction is, in effect, a reversible chemical reaction so that the CVdepends, numerically, upon the concentration of hardness, e.g. calciumions, in the solution to which the chelating agent is added, the pH, andalso the amount of chelating agent which has been added to thatsolution. This is particularly noticeable for chelants with a formationconstant (log K) smaller than 5 (K 10 For these reasons it is desirable,in making practical comparisons of one chelating agent with another, totest them at a constant level of hardness at constant pH and to add eachof the several chelants being tested in an amount that the proportion ofthe hardness which is chelated is the same in each of the severalsamples being tested.

The polyacrylic acid produced by the present process has a chelationvalue (CV) which is normally equal to,

or in excess of, about 500 milligrams of calcium carbonate per gram ofthe polyacrylic acid at an 80% chelation level in an aqueous solutioncontaining a hardness equivalent to 200 ppm of calcium carbonate. Thisis essentially as good as, if not better than, chelation valuescharacteristic of other chclants known to the prior art which, however,have drawbacks of cost, water-pollution tendency, health hazard, oradverse mechanical effects in washing equipment.

The invention will be further illustrated in the following exampleswherein all parts are by weight unless otherwise expressed. It will beunderstood that these examples are given by way of illustration, ratherthan limitation, of the invention. The polyacrylic acid (or its saltsincluding especially alkali metal salts) to the production of which thisinvention is directed will be seen to have very broad applications incombination with surfactants, buffering agents, scouring agents, andother ancillary substances well known in the art, in all enduses inwhich a sequestrant or chelant is customarily employed and includingspecifically such applications as laundry detergents, automaticdishwashing detergents, scouring powders, boiler scale removal, metaldegreasing and cleaning, leather and textile treating solutions, oreleaching and benefication, and ion-exchange operations to name a few.

EXAMPLE I 250 g of 92% acrylic acid, 3.0 g of potassium persulfate, and2.3 g octanethiol were reacted in a 1000 g total aqueous solution for 2hours at 96-98 C. The resulting aqueous polyacrylic acid solution had aviscosity of I25 cps and contained 20.4 weight percent solids. Only 0.4g/l of this polyacrylic acid was required to sequester 94% of Ca ionspresent in a pH 9.5 buffer containing 200 ppm of Ca ions. Expresseddifferently, the polyacrylic acid had the capacity to chelate 560 mgCaCO per gram of polyacrylic acid with 80% of the total calcium presentin the medium being sequestered. The chelation power of some knownsequestering agents under comparable conditions were as follows: citricacid, 350 mg/g; tripolyphosphoric acid, 370 mg/g;ethylenediaminetetraacetic acid, 330 mg/g.

When evaluated under similar conditions, a typical commercialpolyacrylic acid (Versicol E5, from Allied Colloids Co.) required 1.1 gof polyacrylic acid to sequester 95% of the Ca ions present in a pH 9.5buffer containing 200 ppm Ca, corresponding to a chelation capacity of390 mg CaCO /g chelant when 80% of Ca ions have been chelated.

EXAMPLE II 250 g of 92% acrylic acid, 3.0 g of potassium persulfate, and2.3 g butanethiol were reacted in a 1000 g total aqueous solution for 2hours at 96-98 C. The resulting aqueous polyacrylic acid solution had aviscosity of cps and contained 23.9 weight percent solids. Only 0.51 g/lof this polyacrylic acid was required to sequester 95% of the Ca ionspresent in a pH 9.5 buffer containing 200 ppm of Ca ions. Expresseddifferently, the polyacrylic acid had the capacity to chelate 520 mgCaCO per gram of polyacrylic acid with of the total calcium present inthe medium being sequestered.

EXAMPLE III To evaluate the performance of sodium polyacrylate indetergent compositions, formulations A-F listed below were prepared.Formulation F consists of distilled water and serves as a control only.Formulation E in which no builder is utilized contains the surfactantsand the auxiliary components used in a typical heavyduty laundryformulation. Formulations A-D have the builder added to the basicformulation in E and provide a direct comparison between sodiumpolyacrylate and other available builders.

Evaluation of the performance of the formulations was by the wellestablished procedure of Spangler, Journal of the American Oil ChemistsSociety 42, 723-727 (1966). Cotton swatches were uniformly soiled in ablend of synthetic sebum and particulate soil and separated into groupswith similar aggregate de gree of soiling. Measurements of soiling wereperformed with standard commercial reflectometer (Colormaster Model V,Manufacturers Engineering and Equipment Corporation).

The soiled swatches were washed in a standard laboratory Terg-O-Tometer(trade name of US. Testing Company, Hoboken, NJ.) operated at 100 rpm.Five swatches were used for each formulation. One and onehalf grams ofeach of the formulations A-F were used in a liter of water containing160 ppm hardness composed of Ca and 15% Mg. After washing for tenminutes at 120F, the swatches were hand squeezed and put through a 5minute rinse at F. The swatches were next dried in a print dryer, andtheir reflectance determined again. The operation was repeated threetimes (3 cycles). The performance of the formulations in terms ofchanges in reflectance (A Rd) along with the compositions offormulations A-F are shown in the table below:

COMPOSITION WEIGHT A B C D E F Linear alkylbenzene sulfonate 10 IO l0 l0Nonionic surfactant (C -C alcohol ethoxylate 6()'/(") 2 2 l l 2 2 Tallowfatty acids soap 2 2 2 2 Sodium silicate (SiO- :Na O 2.411) 7 7 9 7 7Sodium sulfate 40 40 40 40 Distilled water 4 4 l0 4 39 I00 Sodiumpolyacrylate 35 Sodium tripolyphosphate 35 Sodium carbonate 70 Sodiumoxydiacetate 35 PERFORMANCE (3 cycles) Reflectance, Rd, of soiledswatches I 6L4 60.6 55.0 58.9 58.6 61.2 Reflectance, Rd, of washedswatched 76.9 76.2 69.6 68.l 64.8 65.8

-continued COMPOSlTlON WEIGHT A B I C D E F A RD 15.5 l5.6 14.6 92* 6.24.6

Performed in water of 200 ppm hardness. 60'7: Ca. 4071 Mg -continuedComposition Wt7r r 1 As the detergency results above clea ly nd cate, so10 Sodium mew Silicate l0 drum polyacrylate is an excellent performer inheavy- Trisodium phosphate 5 duty laundry composition. Its closestcompetition, 50- Sodwm polyacrylam 20 Alkylbenzene sulfonate 5 drumtripolyphosphate, is suspected of contributing to eutrophication oflakes and rivers, and its use in laundry detergents is thought by manyto be undesirable.

EXAMPLE IV The formulation given below is suitable for cleaning metalparts prior to use. It cleanses metal-surfaces free of oil and greaseand removes surface scale and rust.

Composition Wt% Sodium silicate (Na sio 24.0 Sodium silicate (sio zNa C)3.1:1) 48.0 Nonionic surfactant (C -C alcohol 1.5 ethoxylate, 607r)Sodium polyacrylate 25.0 Sodium sulfite 1.5

EXAMPLE V Formulation below is a low foaming dishwashing powder withexcellent grease removal and gentle scouring action.

Composition Wt7r Soda ash 5 O The embodiments of the invention in whichan exclu sive property or privilege is claimed are defined as follows:

1. The process for producing a polyacrylic acid of high chelation valueat chelation which comprises polymerizing acrylic acid in aqueoussolution at elevated temperature in the presence of an alkali metal orammonium persulfate as initiator and about 0.5 to 4% by weight ofacrylic acid of a chain transfer agent selected from the groupconsisting of an alkanethiol, a hydroxy alkanethiol and a carboxyalkanethiol.

2. The process of claim 1, wherein the chain transfer agent is analkylmercaptan and is present in a concentration of about 1% by weightof the acrylic acid, and wherein the polymerization is conducted atabout C for about 1 to 2 hours.

3. The process of claim 2, wherein the chain transfer agent isoctanethiol.

4. The process of claim 2, wherein the chain transfer agent isbutanethiol. I

5. The process of claim 1 wherein the chain transfer agent isthioglycolic acid.

6. The process of claim 1 wherein the chain transfer agent is2-thioethanol.

7. Polyacrylic acid produced by the process of claim 2 and having achelation value at 80% chelation in excess of about 500 mg CaCO per gramin an aqueous solution containing calcium ions in a concentrationequivalent to 200 ppm of CaCO Disclaimer 3,904,685.Imj Kfiwtib Shahz'di,Fiorham Park, N.J., and J orge Alberto Blay, Corpus Christi, Tex.POLYACRYLIC ACID HAVING HIGH CHELATION VALUE AND ITS PRODUCTION. Patentdated Sept. 9, 1975. Disclaimer filed Apr. 14:, 1976, by the assignee,Oe-Zamese Oarpomtz'on. Hereby enters this disclaimer to the remainingterm of said patent.

[Ofiiaial Gazette June 1, 1.976.]

1. THE PROCESS FOR PRODUCING A POLYACRYLIC ACID OF HIGH CHELATION VALUEAT 80% CHELATION WHICH COMPRISES POLYMERIZING ACRYLIC ACID IN AQUEOUSSOLUTION AT ELEVATED TEMPERATURE IN THE PRESENCE OF AN ALKALI METAL ORAMMONIUM PERSULFATE AS INITIATOR AND ABOUT 0.5 TO 4% BY WEIGHT OFACRYLIC ACID OF A CHAIN TRANSFER AGENT SELECTED FROM THE GROUPCONSISTING OF AN ALKANETHIOL, A HYDROXY ALKANETHILO AND A CARBOXYALKANETHIOL.
 2. The process of claim 1, wherein the chain transfer agentis an alkylmercaptan and is present in a concentration of about 1% byweight of the acrylic acid, and wherein the polymerization is conductedat about 95* C for about 1 to 2 hours.
 3. The process of claim 2,wherein the chain transfer agent is octanethiol.
 4. The process of claim2, wherein the chain transfer agent is butanethiol.
 5. The process ofclaim 1 wherein the chain transfer agent is thioglycolic acid.
 6. Theprocess of claim 1 wherein the chain transfer agent is 2-thioethanol. 7.Polyacrylic acid produced by the process of claim 2 and having achelation value at 80% chelation in excess of about 500 mg CaCO3 pergram in an aqueous solution containing calcium ions in a concentrationequivalent to 200 ppm of CaCO3.